How large of a water change can I do?

[sds]

My tank has been somewhat neglected for a few months. I think a large water change would be in order. Is there a way to change to much. Doesnt most of the biological bacteria reside in the live rock?
thanks

[Lightsluvr]

In emergencies, such as contamination, I have seen experts recommend 50% changes every day for several days...

If you're just concerned about water quality due to neglected maintenance, I would suggest 20-25% change every few days for a week or so. Then get back on a regular schedule to faithfully change 15% every week.

Remember, your fish are swimming in a sewer. ;)

LL

[Peter Eichler]

Get the specific gravity/salinity and PH close and there's nothing wrong with a 50% or bigger water change. A couple 50% water changes should get your water pretty well situated.

[sds]

Thanks for the help guys i will do a 50 % change and see how that works

[billdogg]

one bigger change is way more effective than several smaller ones for reducing waste (nitrates, etc). 50% or more is not a problem if temp and salinity are the same

[tmz]

50% will work but there is a greater chance of shocking the system than with considerably smaller increments, in my opinion.
Larger changes are more efficient but not by a lot. Neither a large nor small change should effect your nitirfying or denitrifying bacteria unless you fail to keep the rock and substrate submerged.

[pledosophy]

I know aquaculture facilities that do 100% water changes twice a week. Livestock is moved into holding tanks, and then reacclimated.

I have done 50% water changes twice a week for a 6 month period and saw only benefits. I was getting water for free at the time.

[tmz]

Some of my concerns about large changes are: matching temperature and sg; a potential for a bad batch of salt; changes in alkalinity ,calcium and magnesium as fresh elements are added with the salt mix; changes in the levels of minor and trace elements which also come in with the unaged salt mix some of which are toxic at high levels (such as copper aluminum and zinc) .A little time is required for some of these to precipitate or to be taken up as organics.

Having said that large changes are necessary from time to time and will alleviate many water quality issues, quickly.